We are examining the biochemical basis for desensitization to a variety of bone-active hormones produced in isolated osteoclast-like and osteoblast-like bone cells that are obtained from mouse calvaria. We are at the same time developing a series of biochemical markers of bone cell activity in order to evaluate the mechanisms of bone cell growth and function. In order to aid in this study we are also working with intact bone and isolated bone cells from an animal model of osteopetrosis--the micropthalmic mouse--whose intact bone exhibits a blunted response to calcitonin.